Character customization options to be unlocked via Operations

In Ghosts, challenges have been renamed to ‘Operations.’ Completing these operations you will unlock new character customization options in game. You can unlock new head gear, body wear, masks, colors, and so much more.

For your weapons, you unlock these using Squad Points. You earn squad points as you play the game. You chose what you want to unlock when you want. There’s no specific level to reach for anything.

SOURCE: GameInformer